Drivers’ memo #8: Travel efficiency in town and country, and differences between models

This month’s example of how we will use your results focuses on travel efficiency. Measures of efficiency (Km per kWh) of your EVs and PHEVs are important for the various equations that estimate cost, environmental benefits and energy demand. Efficiency is also a key component of the all-important maximum range between charges. We don’t yet have enough data to make definitive estimates, but analysis of the efficiency of 38 fully electric vehicles from recent months showed:

Efficiency increased by around 17% for vehicles doing nearly all their travel within 50kph zones, compared to those driving almost entirely in ‘non-urban’ areas (See Figure 1 in the attachment).

This is the opposite of the effect seen in Internal Combustion Vehicles which use about 49% more fuel per km when driven in town compared to along the open road. In an increasingly urbanised NZ, it makes great sense from straight energy efficiency to flip the fleet!

We suppose the increased efficiency in towns is partly a result of EVs recovering energy during breaking, efficient acceleration, not using energy when stopped in a traffic jam, and not travelling as fast as on the open road (friction and energy required to displace the air escalates with increasing speed).

EV vans (eNV200s in our panel) have lowest efficiency, presumably because they have a less aerodynamic shape, displace a larger volume of air, and may often be loaded with goods (see Figure 2 in the attached).

The Gen 2 Leaf average efficiency is 7% higher than for Gen 1s. We need more data to confirm the size of the difference, but some gain is expected by the reduced kerb weight, and more efficient accessories of the Gen 2.

As we grow the Flip the Fleet panel, we should be able to make all sorts of comparisons of the financial benefits, return on investment, environmental gains etc. of the various LEV models in NZ. Variation will probably also be regional and reflect terrain (hills suck energy!)